Simple Solutions That Work! Issue 9

34 Figure 3. Feeder contacts with original design (2 feeders). To resolve this problem, it was decided to analyze this casting using the approach described previously to determine the feeding requirements. First, a solidification simulation of the casting without gating or feeders was performed. The data from the simulation was converted to Modulus data so that the feeding calculations can be performed. Figure 4 shows a plot of the areas of highest Modulus in the casting. From viewing this plot, the foundry engineer might be tempted to conclude that the original feeder design was correct, as there are two areas of high Modulus value in the casting and these are adjacent to the feeder contacts in the original design. However, it is necessary to further analyze this casting to determine the Shrinkage Time and from this the Transfer Modulus (MTR) in order to understand the location and size of the feeding zones within the casting. Figure 5 shows the calculation performed within the software of values for both ST and MTR. Analysis of the iron characteristics for this casting indicates that the value of the Transfer Modulus is 0.645 cm. Creating a plot of this value within the casting will indicate the location of feed zone(s); this is shown in Figure 6. This plot shows that the entire casting is a single feed zone. The areas of higher modulus are connected by a section of the casting in which the Modulus is above the value of MTR, allowing liquid transport for feeding throughout the casting. This means that only a single feeder should be used on this casting. With the two-feeder design, both feeders were connected to the same zone of the casting; when this is done, one feeder will pipe and the other feeder will not pipe, resulting in porosity at the contact of the non-piping feeder. It should be noted that the computer simulation in this case took 16 minutes to perform, and within less than 5 minutes after that the calculation of ST, MTR, and the plot shown in Figure 8 were created. This means that with about 20 minutes of analysis, the correct feeder design was arrived at. Had this been done before the original pattern equipment was created, several months of time involved with production of defective castings would have been avoided. The costs involved were far greater than the cost of the software and training to perform this analysis. After this information was presented to the foundry, the pattern was revised to reflect a single feeder as shown in Figure 7. It should be noted that the feeder in this case is not connected to the casting at one of the areas of high Modulus. This illustrates the point that in iron castings, the location of the feeder is not as critical as in steel castings. This is due to the expansion pressure which acts throughout the casting once precipitation of graphite begins. Finally, Figure 8 shows a photograph of the contact area with a single feeder. In this case there is no porosity at the feeder contact, and no porosity elsewhere within the casting. Thus, a simple and quick analysis of the casting has produced the correct feeder design for making a sound casting. Figure 4. Areas of high modulus value in the casting.